| Year | Value | | 2022 | 5.6391667139637 | | 2021 | 7.3468144053353 | | 2020 | 5.6293652263251 | | 2019 | 2.7264303738882 | | 2018 | 2.7239638618372 | | 2017 | 4.9550836698513 | | 2016 | 3.2198868939572 | | 2015 | 4.5481439508221 | | 2014 | 8.2710609394933 | | 2013 | 8.7763834526821 | | 2012 | 10.919656944683 | | 2011 | 8.848985699468 | | 2010 | 7.0363831607302 | | 2009 | 4.361122191198 | | 2008 | 8.3271604938271 | | 2007 | 5.1561113875846 | | 2006 | 5.0004543802254 | | 2005 | 5.3126310463775 | | 2004 | 4.1059369827296 | | 2003 | 2.5723086169333 | | 2002 | 2.4553571428572 | | 2001 | 3.414789461116 | | 2000 | 4.0121208107034 | | 1999 | 6.7769939355363 | | 1998 | 10.585589989246 | | 1997 | 6.5054871826909 | | 1996 | 8.7900138193516 | | 1995 | 9.4875483678937 | | 1994 | 7.0099535500995 | | 1993 | 11.198016587468 | | 1992 | 15.975217361539 | | 1991 | 12.275172943889 | | 1990 | 10.011838322341 | | 1989 | 8.7798371889803 | | 1988 | 10.096713757659 | | 1987 | 6.3317719269909 | | 1986 | 9.9644760213143 | | 1985 | 1.8820123054651 | | 1984 | 7.0377066115702 | | 1983 | 18.057778794115 | | 1982 | 9.846772167797 | | 1981 | 9.9723756906077 |
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